Option Explicit
Sub BoldString()
Dim lRw As Long, Ff As Long
Dim BDau As Byte, KThuc As Integer
lRw = [b65500].End(xlUp).Row
For Ff = 2 To lRw
With Cells(Ff, "B")
BDau = InStr(1, .Value, Chr(10))
If BDau > 0 Then
KThuc = InStr(BDau + 1, Cells(Ff, "B"), Chr(10))
With .Characters(Start:=BDau, Length:=KThuc - BDau).Font
.FontStyle = "Bold"
End With
End If
End With
Next Ff
End Sub